Atomic Scale Surface Segregation in Copper-Gold Nanoparticles

TL;DR

This study combines microscopy and atomistic simulations to analyze gold surface segregation in Cu-Au nanoparticles, revealing atomic-level segregation patterns and their implications for catalytic properties.

Contribution

It provides the first atomic-scale investigation of gold segregation in Cu-Au nanoparticles, combining experimental measurements with Monte Carlo simulations.

Findings

Gold segregates to the surface in Cu-Au nanoparticles above certain compositions.

Segregation behavior is consistent across different nanoparticle sizes.

Surface segregation influences catalytic reactivity and stability.

Abstract

In this work, we combine electron microscopy measurements of the surface compositions in Cu-Au nanoparticles and atomistic simulations to investigate the effect of gold segregation. While this mechanism has been extensively investigated within Cu-Au in the bulk state, it was never studied at the atomic level in nanoparticles. By using energy dispersive X-ray analysis across the (100) and (111) facets of nanoparticles, we provide evidence of gold segregation in Cu$_{3}$Au and CuAu$_{3}$ nanoparticles in the 10 nm size range grown by epitaxy on a salt surface with high control of the nanoparticles morphology. To get atomic-scale insights into the segregation properties in Cu-Au nanoparticles on the whole composition range, we perform Monte Carlo calculations employing $N$-body interatomic potentials. These simulations confirm this effect by showing a complete segregation of Au in the (100) and (111) faces of a truncated octahedron for gold nominal composition of the alloy above 70\% and 60\% respectively. Furthermore, we show that there is no size effect on the segregation behaviour since we evidence the same oscillating concentration profile from surface to the nanoparticles core as in the bulk. These results can shed new lights in the interpretation of the enhanced reactivity, selectivity and stability of Cu-Au nanoparticles in various catalytic reactions.